Pandas help!

I have a specific column like this,

   Mpg
0   18
1   17
2   19
3   21
4   16
5   15

Mpg is mile per gallon, Now I need to replace that 'MPG' column to 'litre per 100 km' and change those values to litre per 100 km' at the same time. Any help? Thanks beforehand. -Tom

I changed the name of the column but doing both simultaneously,i could not.

CodePudding user response：

Use pop to return and delete the column at the same time and rdiv to perform the conversion (1 mpg = 1/235.15 liter/100km):

df['litre per 100 km'] = df.pop('Mpg').rdiv(235.15)

If you want to insert the column in the same position:

df.insert(df.columns.get_loc('Mpg'), 'litre per 100 km',
          df.pop('Mpg').rdiv(235.15))

Output:

   litre per 100 km
0         13.063889
1         13.832353
2         12.376316
3         11.197619
4         14.696875
5         15.676667

CodePudding user response：

An alternative to pop would be to store the result in another dataframe. This way you can perform the two steps at the same time. In my code below, I first reproduce your dataframe, then store the constant for conversion and perform it on all entries using the apply method.

df = pd.DataFrame({'Mpg':[18,17,19,21,16,15]})

cc = 235.214583 # constant for conversion from mpg to L/100km

df2 = pd.DataFrame()
df2['litre per 100 km'] = df['Mpg'].apply(lambda x: cc/x)

print(df2)

The output of this code is:

   litre per 100 km
0        13.067477
1        13.836152
2        12.379715
3        11.200694
4        14.700911
5        15.680972

as expected.